Light emitting device having a layer with a metal oxide and a benzoxazole derivative

ABSTRACT

It is an object of the present invention to provide a light-emitting device that is high in color purity of light and is high in light extraction efficiency, where sputtering is used to form an electrode on an electroluminescent layer without damage to a layer including an organic material. 
     The present invention provides a light-emitting device comprising a first light-emitting element that emits red light, a second light-emitting element that emits green light, a third light-emitting element that emits blue light, and a color filter, where the color filter comprises a first coloring layer that selectively transmits red light, a second coloring layer that selectively transmits green light, and a third coloring layer that selectively transmits blue light, the first to third light-emitting elements respectively correspond to the first to third coloring layers, wherein each of the first to third light-emitting elements has a first electrode, an electroluminescent layer formed on the first electrode, and a second electrode formed on the electroluminescent layer, and wherein the electroluminescent layer includes a layer in contact with the second electrode, and a metal oxide or a benzoxazole derivative is included in the layer in contact with the second electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting device that has alight-emitting element in each pixel.

2. Description of the Related Art

A light-emitting element itself emits light with high visibility, needsno backlight that is required for a liquid crystal display device (LCD)to be suitable for reduction in thickness, and has no limit of viewingangle. Therefore, a light-emitting device using a light-emitting elementhas been attracting attention as an alternative display device to a CRTor an LCD, and has been putting into practical use. An OLED (OrganicLight Emitting Diode) that is one of light-emitting elements has a layerincluding an electroluminescent material from which luminescence(electroluminescence) can be obtained by applying an electric field(hereinafter, referred to as an electroluminescent layer), an anode, anda cathode. By combining a hole injected from the anode and an electroninjected from the cathode in the electroluminescent layer, luminescencecan be obtained. The luminescence that can be obtained from theelectroluminescent layer includes luminescence (fluorescence) onreturning to the ground state from a singlet excited state andluminescence (phosphorescence) on returning to the ground state from atriplet excited state.

The obtained light can be extracted from any of the anode side and thecathode side in principle. In the case of an active matrixlight-emitting device, it is preferable that the light is extracted fromthe electrode, the anode or the cathode on the side that is farther awayfrom a substrate over which a wiring or a gate electrode of a transistoris formed since a high extraction efficiency can be kept independentlyof a decrease in aperture ratio with high resolution. The light can beextracted from the electrode by using either method of forming theelectrode thinly enough to transmit light or forming the electrode withthe use of a transparent conductive film. However, in the former methodof the above-mentioned two methods, it is difficult to enhance a lightextraction efficiency sufficiently since transmissivity has a limit.

On the other hand, in the case of using the latter method, it isrelatively easy to enhance a light extraction efficiency as compared theformer.

However, when sputtering is used to form a transparent conductive filmtypified by ITO (Indium Tin Oxide) on an electroluminescent layer, thereis a problem that a layer including an organic material is subjected todamage (sputter damage) in the electroluminescent layer. In the case ofusing evaporation to form a transparent conductive film, damage to thelayer including the organic material can be suppressed. However, in thiscase, an electrode to be formed is reduced in transmissivity and isincreased in resistivity, which is undesirable. Now therefore, it isdesired to propose a light-emitting device, where sputtering is used toform an electrode on an electroluminescent layer without damage to alayer including an organic material.

In order to perform displaying in full color with a light-emittingdevice, a method of using three kinds of light-emitting elementscorresponding to R (red), G (green), and B (blue) or a method ofcombining a light-emitting element that emits white light and a colorfilter is generally used. However, in the case of the former method, itis necessary to enhance the color purity of luminescence correspondingto each of R (red), G (green), and B (blue), and then spend a lot ofcost and time to optimize an electroluminescent material and a devicestructure. In the case of the latter method, light shielded by the colorfilter is wasted, and then, there is a problem that no high luminancecan be obtained for the power consumption.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems, it is an object of the presentinvention to provide a light-emitting device that is high in colorpurity of light and is high in light extraction efficiency, wheresputtering is used to form an electrode on an electroluminescent layerwithout damage to a layer including an organic material.

In the present invention, a material that is resistant to etching isused for a layer of an electroluminescent layer, which is closest to anelectrode that is formed by sputtering on the electroluminescent layer.Specifically, using at least one of a metal oxide and a benzoxazolederivative is advised.

Specific examples of the metal oxide include molybdenum oxide (MoOx),vanadium oxide (VOx), ruthenium oxide (RuOx), and tungsten oxide (WOx),and it is preferred that these are formed by evaporation. In addition,the structure of the benzoxazole derivative is represented by ChemicalFormula 1.

(where Ar is an aryl group, and R1 to R4 are individually hydrogen,halogen, a cyano group, an alkyl group having 1 to 10 carbon atoms, ahaloalkyl group having 1 to 10carbon atoms, an alkoxyl group having 1 to10 carbon atoms, a substituted or unsubstituted aryl group, or asubstituted or unsubstituted heterocyclic group.)

A light-emitting element according to the present invention has a firstelectrode, an electroluminescent layer formed on the first electrode, asecond electrode formed on the electroluminescent layer, where theelectroluminescent layer may be a single layer or a multilayer, and hasa layer from which luminescence can be actually obtained (alight-emitting layer) appropriately in combination with a layer such asa layer including a highly carrier (electron/hole) transporting materialor a layer including a highly carrier injecting material.

For example, in the case where the first electrode serves as a cathodeand the second electrode serves as an anode, the above-mentionedmaterial that is resistant to etching is used for a hole injecting orhole transporting layer of the electroluminescent layer, which isclosest to the anode. Specifically, in the case of using a benzoxazolederivative, a layer including the benzoxazole derivative and one or morematerials of tetracyanoquinodimethane (TCNQ), FeCl₃, C₆₀, and2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄-TCNQ) is formedto be closest to the anode.

Alternatively, in the case where the first electrode serves as an anodeand the second electrode serves as a cathode, for example, theabove-mentioned material that is resistant to etching is used for anelectron injecting or electron transporting layer of theelectroluminescent layer, which is closest to the cathode. Specifically,in the case of using molybdenum oxide, a layer including the molybdenumoxide and one or more materials of an alkali metal, an alkali earthmetal, and a transition metal is formed to be closest to the cathode. Inthe case of using a benzoxazole derivative, a layer including thebenzoxazole derivative and one or more materials of an alkali metal, analkali earth metal, and a transition metal is formed to be closest tothe cathode. Both the metal oxide and the benzoxazole derivative may beused.

According to the above-mentioned aspect of the present invention, evenwhen a transparent conductive film formed by sputtering, for example,indium tin oxide (ITO), Indium Tin Oxide containing silicon (ITSO), orIZO (Indium Zinc Oxide) of indium oxide mixed with zinc oxide (ZnO) at 2to 20% is used as the second electrode, sputter damage to a layerincluding an organic material of the electroluminescent layer can besuppressed, and then, the material for forming the second electrode hasa wide range of choice. Further, in the present invention, the lightextraction efficiency can be enhanced by extracting light from thesecond electrode side as compared with a case of extracting light fromthe first electrode side.

It is often the case that a spectrum of light obtained from alight-emitting element has a peak in a relatively wide wavelength range.Therefore, there is a problem that the color purity is inferior.Further, not only color purity but also reliability is required to behigh as for characteristics of a light-emitting element. However, thepresent situation is spending a lot of time and cost to develop andobtain a light-emitting element that meets the both characteristicssufficiently. Consequently, in a light-emitting device according to thepresent invention, a plurality of light-emitting elements that havedifferent wavelength ranges in emitting light and a color filter areused to extract only light in a specific wavelength range of lightemitted from each of the light-emitting elements. According to theabove-mentioned aspect of the present invention, even when alight-emitting element that has a relatively wide wavelength range isused, an unnecessary wavelength of light obtained from thelight-emitting element is shielded by a color filter to enableextracting only a necessary wavelength range, hence it is easy to obtaina high color purity. Therefore, the electroluminescent material that isused for the light-emitting element is allowed to have a wide range ofchoice. In addition, the amount of light to be shielded by a colorfilter can be suppressed by selecting an electroluminescent material inaccordance with a wavelength of light to be extracted as compared with acase of combining a light-emitting element that emits white light and acolor filter, and the extraction efficiency can be enhanced.

The light-emitting device according to the present invention is notlimited to an active matrix light-emitting device, and may be a passivematrix light-emitting device.

As described above, according to the present invention, sputtering canbe used to form an electrode on an electroluminescent layer withoutdamaging a layer including an organic material, hence it is possible toprovide a light-emitting device where a defect due to sputter damage issuppressed. Therefore, the material of the electrode to be formed on theelectroluminescent layer is allowed to have a wide range of choice. Inaddition, a color purity of light can be easily enhanced by using acolor filter, and a light extraction efficiency can be enhanced ascompared to a case of combining a white light-emitting element and acolor filter. Further, since it becomes possible to give priority tocharacteristics other than color purity, such as reliability, to someextent, the electroluminescent material is allowed to have a wide rangeof choice.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are diagrams showing schematically a relationshipbetween a color of light emitted from a light-emitting element and acolor of light transmitted through a coloring layer;

FIG. 2 is a cross-sectional view of a light-emitting device according tothe present invention;

FIG. 3 is a diagram showing a structure of a light-emitting element in alight-emitting device according to the present invention;

FIGS. 4A and 4B are top views of a pixel of a light-emitting deviceaccording to the present invention;

FIGS. 5A to 5C are diagrams showing a relationship between a wavelengthof light and a transmissivity with respect to a coloring layer;

FIGS. 6A to 6C are diagrams showing structures of a light-emittingelement in a light-emitting device according to the present invention;

FIG. 7 is a cross-sectional view of a light-emitting device according tothe present invention;

FIG. 8 is a cross-sectional view of a light-emitting device according tothe present invention;

FIG. 9 is a cross-sectional view of a light-emitting device according tothe present invention;

FIGS. 10A and 10B are cross-sectional views of light-emitting devicesaccording to the present invention;

FIGS. 11A and 11B are cross-sectional views of light-emitting devicesaccording to the present invention;

FIG. 12 is a cross-sectional view of a light-emitting device accordingto the present invention;

FIGS. 13A and 13B are a top view and a cross-sectional view of alight-emitting device according to the present invention; and

FIGS. 14A to 14C are diagrams of electronic devices using alight-emitting device according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A structure of a light-emitting device according to the presentinvention will be described. The light-emitting device according to thepresent invention has a plurality of pixels corresponding to threeprimary colors, for example, red (R), green (G), blue (B), and a colorfilter. Each of the pixels has a light-emitting element, and lightemitted from the light-emitting element includes at least a wavelengthof a color corresponding to the pixel. However, light emitted from thelight-emitting element does not always have the same spectrum as theothers.

In the present invention, a layer that has a particularly hightransmissivity to light in a specific wavelength range as compared tothe other range (a coloring layer), which is included in the colorfilter, is used to shield light in a specific wavelength range of lightemitted from each light-emitting element. In the case of light emittedfrom the light-emitting element of the pixel corresponding to a red, forexample, light in the wavelength range corresponding to the red iscontrolled to be selectively transmitted by the coloring layer. Also inthe pixel corresponding to the other color, light in the wavelengthrange corresponding to the corresponding color is transmittedselectively in the same way.

FIG. 1A schematically shows a relationship between a color of lightemitted from a light-emitting element and a color of light transmittedthrough a coloring layer. In FIG. 1A, reference numeral 101 denotes alight-emitting element of a pixel corresponding to a red, and lightemitted from the light-emitting element 101 is presumed to include lightof a color (α) other than the red (R) in addition to light of the red.Similarly, reference numeral 102 denotes a light-emitting element of apixel corresponding to a green, and light emitted from thelight-emitting element 102 is presumed to include light of a color (β)other than the green (G) in addition to light of the green. Referencenumeral 103 denotes a light-emitting element of a pixel corresponding toa blue, and light emitted from the light-emitting element 103 ispresumed to include light of a color (γ) other than the blue (B) inaddition to light of the blue.

Further, a coloring layer corresponding to each pixel is shown in FIG.1A. Specifically, a coloring layer 104 corresponding to thelight-emitting element 101, a coloring layer 105 corresponding to thelight-emitting element 102, and a coloring layer 106 corresponding tothe light-emitting element 103 are shown in the figure.

The coloring layer 104 is able to transmit light in the wavelength rangecorresponding to the red selectively. In other words, since the light ofthe color (α) other than the red, of the light emitted from thelight-emitting element 101, is shielded, only the light of the red canbe selectively extracted. Similarly, the coloring layer 105 is able totransmit light in the wavelength range corresponding to the greenselectively. In other words, since the light of the color (β) other thanthe green, of the light emitted from the light-emitting element 102, isshielded, only the light of the green can be selectively extracted. Inaddition, the coloring layer 106 is able to transmit light in thewavelength range corresponding to the blue selectively. In other words,since the light of the color (γ) other than the blue, of the lightemitted from the light-emitting element 103, is shielded, only the lightof the blue can be selectively extracted.

Accordingly, the color purity of light extracted from the pixel can beenhanced with the above-mentioned structure, even when the color purityof light emitted from each of the light-emitting elements 101 to 103 isinferior in some degree. As for the light-emitting element of the pixelcorresponding to each color, it is preferable that the spectrum of lightemitted from the light-emitting element has a peak with relatively highintensity in the wavelength range corresponding to the color as comparedwith the other wavelength range. For example, in the case of the pixelcorresponding to the red, it is preferable that the spectrum of lightemitted from the light-emitting element is controlled to have a peakwith relatively high intensity in the wavelength range corresponding tothe red. With the above-mentioned structure, the amount of light to beshielded can be suppressed with respect to the pixel corresponding toeach color, and light can be efficiently extracted as compared with acase of using a light-emitting element that emits white light.

FIG. 1A shows an example where light obtained from a light-emittingelement has a different spectrum depending on a pixel corresponding toeach color. However, the present invention is not limited to thisstructure. For example, among pixels corresponding to three colorsrespectively, the pixels corresponding to the two colors may havelight-emitting elements from which the same spectrum of light can beobtained respectively.

With reference to FIG. 1B, a structure according to the presentinvention will be described, where a light-emitting element of a pixelcorresponding to a red and a light-emitting element of a pixelcorresponding to a green have the same spectrum of light. In FIG. 1B,reference numeral 111 denotes a light-emitting element of a pixelcorresponding to a red and reference numeral 112 denotes alight-emitting element of a pixel corresponding to a green, lightemitted from each of the light-emitting elements 111 and 112 is presumedto include light of the red (R) and light of the green (G). In addition,reference numeral 113 denotes a light-emitting element of a pixelcorresponding to a blue, and light emitted from the light-emittingelement 113 is presumed to include light of a color (δ) other than theblue (B) in addition to light of the blue.

Further, a coloring layer corresponding to each pixel is shown in FIG.1B. Specifically, a coloring layer 114 corresponding to thelight-emitting element 111, a coloring layer 115 corresponding to thelight-emitting element 112, and a coloring layer 116 corresponding tothe light-emitting element 113 are shown in the figure.

The coloring layer 114 is able to transmit light in the wavelength rangecorresponding to the red selectively. Therefore, since the light of thegreen (G), of the light emitted from the light-emitting element 111, isshielded, only the light of the red (R) can be selectively extracted.Similarly, the coloring layer 115 is able to transmit light in thewavelength range corresponding to the green selectively. In other words,since the light of the red (R), of the light emitted from thelight-emitting element 112, is shielded, only the light of the green (G)can be selectively extracted. In addition, the coloring layer 116 isable to transmit light in the wavelength range corresponding to the blueselectively. In other words, since the light of the color (δ) other thanthe blue, of the light emitted from the light-emitting element 113, isshielded, only the light of the blue can be selectively extracted.

As described above, an electroluminescent material is allowed to have asubstantially wide range of choice in the present invention.

Next, a more specific structure of a light-emitting device according tothe present invention will be described with reference to FIG. 2. FIG. 2shows a form of a cross-sectional view of a pixel in a light-emittingdevice according to the present invention. In FIG. 2, TFTs 201 to 203and light-emitting elements 204 to 206 are formed over a substrate 200.The TFT 201 and the light-emitting element 204 are provided in a pixelcorresponding a red (R), and the current supply to the light-emittingelement 204 is controlled by the TFT 201. The TFT 202 and thelight-emitting element 205 are provided in a pixel corresponding a green(G), and the current supply to the light-emitting element 205 iscontrolled by the TFT 202. The TFT 203 and the light-emitting element206 are provided in a pixel corresponding a blue (B), and the currentsupply to the light-emitting element 206 is controlled by the TFT 203.

Further, reference numeral 207 denotes a covering material for sealingof the light-emitting elements 204 to 206, which has alight-transmitting property. Adjacent to the covering material 207, acolor filter 212 that has a shielding film 208 for shielding visiblelight and coloring layers 209 to 211 corresponding the pixelscorresponding the respective colors is formed. In the case of FIG. 2,light in the wavelength range corresponding to the red, of light emittedfrom the light-emitting element 204, is selectively transmitted throughthe coloring layer 209, light in the wavelength range corresponding tothe green, of light emitted from the light-emitting element 205, isselectively transmitted through the coloring layer 210, and light in thewavelength range corresponding to the blue, of light emitted from thelight-emitting element 206, is selectively transmitted through thecoloring layer 211.

The shielding film 208 is arranged to overlap a portion between thelight-emitting elements, such as a portion between the light-emittingelements 204 and 205 and a portion between the light-emitting elements205 and 206, and is able to prevent light from the light-emittingelement from being transmitted through the coloring layer correspondingto the adjacent pixel.

For the coloring layer, a material that is generally used can be used.For example, a pigment is dispersed in a light-transmitting organicmaterial such as a resin to form the coloring layer. In addition, amaterial that is generally used can be used for the shielding film. Ametal typified by Cr may be used to form the shielding film, or a blackpigment is dispersed in a light-transmitting organic material such as aresin to form the shielding film. Further, inkjet may be used to formthe coloring layer adjacent to the covering layer.

The light-emitting element 204 has a first electrode 213 electricallyconnected to the TFF 201, an electroluminescent layer 214 formed on thefirst electrode 213, and a second electrode 215 formed on theelectroluminescent layer 214, and a portion where the first electrode213, the electroluminescent layer 214, and the second electrode 215 areoverlapped with each other corresponds to the light-emitting element204.

The light-emitting element 205 has a first electrode 216 electricallyconnected to the TFT 202, an electroluminescent layer 217 formed on thefirst electrode 216, and the second electrode 215 formed on theelectroluminescent layer 217, and a portion where the first electrode216, the electroluminescent layer 217, and the second electrode 215 areoverlapped with each other corresponds to the light-emitting element205.

The light-emitting element 206 has a first electrode 218 electricallyconnected to the TFT 203, an electroluminescent layer 219 formed on thefirst electrode 218, and the second electrode 215 formed on theelectroluminescent layer 219, and a portion where the first electrode218, the electroluminescent layer 219, and the second electrode 215 areoverlapped with each other corresponds to the light-emitting element206.

In FIG. 2, the electroluminescent layer 214, 217, or 219 that has adifferent electroluminescent material included or a different elementstructure is used depending on the pixel corresponding to each color.However, the present invention is not always limited to this structure.In at least pixels corresponding to two colors respectively,electroluminescent layers that have different electroluminescentmaterials included or different element structures from each other areused respectively.

In the present invention, a transparent conductive film such as ITO,ITSO, or IZO, mentioned above, is used for the second electrode 215formed on the electroluminescent layers 214, 217, and 219, which isformed by sputtering. In each of the electroluminescent layers 214, 217,and 219, the top layer in contact with the second electrode 215 includesat least one of a metal oxide and a benzoxazole derivative.

Next, a structure of a light-emitting element according to the presentinvention will be described with reference to FIG. 3. FIG. 3schematically shows a structure of a light-emitting element according tothe present invention. A light-emitting element 301 according to thepresent invention has a first electrode 302 formed over a substrate 300,a second electrode 303, and an electroluminescent layer 304 providedbetween the first electrode 302 and the second electrode 303. Inpractice, components such as various layers or a semiconductor elementare provided between the substrate 300 and the light-emitting element301.

One of the first electrode 302 and the second electrode 303 correspondsto an anode, and the other corresponds to a cathode. In FIG. 3, thefirst electrode 302 serves as a cathode, and the second electrode 303serves as an anode. Further, in the present invention, a material thatis resistant to etching by sputtering, such as a metal oxide or abenzoxazole derivative, is included in a layer 305 of theelectroluminescent layer 304, which is closest to the second electrode303 formed on the electroluminescent layer 304. Specifically, FIG. 3shows an example where the second electrode 303 serves as an anode.Therefore, in order to give a hole injecting property to the layer 305that is closest to the second electrode 303, in the case of using abenzoxazole derivative, the benzoxazole derivative and one or morematerials of TCNQ, FeCl₃, C₆₀, and F₄-TCNQ are included in the layer305.

As the metal oxide, molybdenum oxide (MoOx), vanadium oxide (VOx),ruthenium oxide (RuOx), and tungsten oxide (WOx), for example, can beused. By using the metal oxide or the benzoxazole derivative in thisway, sputter damage to a layer including an organic material, of theelectroluminescent layer 304, can be suppressed when the secondelectrode 303 is formed by sputtering. Both in the case of including themetal oxide and in the case of including the benzoxazole derivative, thelayer 305 that is closest to the second electrode 303 can be formed byusing evaporation. In addition, an effect of suppressing damage due tosputtering can be enhanced by controlling the film thickness of thelayer 305 to be 10 nm or more.

Contrary, in the case where the first electrode 302 serves as an anodeand the second electrode 303 serves as a cathode, in order to give anelectron injecting property to the layer 305 that is closest to thesecond electrode 303, the layer 305 include one or more materials of analkali metal, an alkali earth metal, and a transition metal in the caseof using any of a metal oxide and a benzoxazole derivative.

In the light-emitting device according to the present invention, theshielding film of the color filter is able to prevent the firstelectrode from reflecting outside light to reflect an object into thepixel portion like a mirror surface. Therefore, it is not necessary touse a polarizing plate that has a significantly low transmissivity ascompared with the color filter, and a light extraction efficiency can beenhanced spectacularly. In addition, a decrease in extraction efficiencydue to attenuation of light is not caused by using a structure such as amicro cavity in order to enhance a color purity.

EMBODIMENT 1

In the present embodiment, a form of how to lay out a light-emittingelement and a coloring layer and shielding film of a color filter willbe described.

FIG. 4A shows a top view of a pixel of a light-emitting device accordingto the present invention. However, FIG. 4A shows a state before sealingwith a covering material, where reference numerals 401 to 403 denotelight-emitting elements and reference numeral 404 denotes a wiring forcontrolling a supply of a signal or a power supply voltage to a pixel.Further, various interlayer films and a partition are omitted in thefigure. In the present embodiment, the light-emitting element 401 ispresumed to be formed in a pixel corresponding a red (R), thelight-emitting element 402 is presumed to be formed in a pixelcorresponding a green (G), and the light-emitting element 403 ispresumed to be formed in a pixel corresponding a blue (B).

FIG. 4B then shows a state where the pixels shown in FIG. 4A areencapsulated with a cover material. Reference numeral 405 denotes ashielding film, which is arranged to fill a portion between thelight-emitting elements, such as a portion between the light-emittingelements 401 and 402 and a portion and between the light-emittingelements 402 and 403. In addition, reference numerals 406 to 408 denotecoloring layers, which are formed respectively in opening portions ofthe shielding film 405. Of light emitted from the light-emitting element401, light in the wavelength range corresponding to the red can beextracted selectively by the coloring layer 406. Of light emitted fromthe light-emitting element 402, light in the wavelength rangecorresponding to the green can be extracted selectively by the coloringlayer 407. Of light emitted from the light-emitting element 403, lightin the wavelength range corresponding to the blue can be extractedselectively by the coloring layer 408.

EMBODIMENT 2

In the present embodiment, the mechanism of an improvement in colorpurity by a color filter will be described.

FIG. 5A shows a relationship between a wavelength of light and atransmissivity with respect to a coloring layer as an example. In FIG.5A, the wavelength range that has shorter wavelengths than 600 nm ismuch lower in transmissivity than the wavelength range that has longerwavelengths than 600 nm.

Further, FIG. 5B shows a spectrum in the case of light in the wavelengthrange corresponding to a red, which is mixed with light in thewavelength range corresponding to a green. The spectrum shown in FIG. 5Bhas a small shoulder from 550 nm to 600 nm in addition to a peak in thewavelength range corresponding to the red including 700 nm. The lightwith this spectrum is low in purity of the red, and seems to be greenishred.

Then, by transmitting the light with the spectrum shown in FIG. 5Bthrough the coloring layer that has the characteristics shown in FIG.5A, light with a spectrum shown in FIG. 5C can be obtained.Specifically, the shoulder of the spectrum in FIG. 5B is almost entirelyreduced since light including a wavelength of 600 nm or less, which isclose to the wavelength region corresponding to the green including 546nm, is shielded. Accordingly, the light extracted through the coloringlayer is improved in color purity of the red.

The wavelength range corresponding to each of a red, a green, and a bluecan be determined appropriately in accordance with a color puritydesired by a designer. In the case of requiring a higher color purity,the width of the wavelength range corresponding the color may benarrowed.

EMBODIMENT 3

In the present embodiment, a specific example of a light-emittingelement of a light-emitting device according to the present inventionwill be described.

With reference to FIG. 6A, a structure of a light-emitting element fromwhich light in the wavelength range corresponding to a blue can beobtained will be described. The light-emitting element shown in FIG. 6Ahas, over a substrate 600, a first electrode 601, an electroluminescentlayer 602 formed on the first electrode 601, and a second electrode 603formed on the electroluminescent layer 602. In FIG. 6A, the firstelectrode 601 serves as a cathode and the second electrode 603 serves asan anode.

In the present invention, a metal, an alloy, an electrically conductivecompound, and a mixture of these, which have a small work function andare generally used for a cathode of a light-emitting element, can beused to form the first electrode 601. Specifically, in addition to analkali metal such as Li or Cs, an alkali earth metal such as Mg, Ca, orSr, and an alloy including the metal (such as Mg:Ag or Al:Li), arare-earth metal such as Yb or Er can also be used to form the firstelectrode 601. Further, a common conductive film such as aluminum canalso be used since a layer including a highly electron injectingmaterial is formed to come in contact with the first electrode 601.

It is preferable that a conductive material that has a large workfunction is used to form the second electrode 603. In the case oftransmitting light through the second electrode 603, a highlylight-transmitting material is used. In this case, a transparentconductive film such as indium-tin oxide (ITO), indium-zinc oxide (IZO),or indium-tin oxide including silicon oxide (ITSO) may be used.

Further, in FIG. 6A, the electroluminescent layer 602 has first to fifthlayers 604 to 608. It is preferable that a highly electron injectingmaterial is used for the first layer 604 formed to come in contact withthe first electrode 601 that serves as a cathode. Specifically, an ultrathin film including an insulator such as an alkali metal halide such asLiF or CsF, an alkali earth halide such as CaF₂, or an alkali metaloxide such as Li₂O is often used. In addition, alkali-metal complexessuch as lithium acetyl acetonate (abbreviation: Li(acac)) and8-quinolinolato-lithium (abbreviation: Liq) are also efficient. Further,the first layer 604 may include one of a metal oxide such as molybdenumoxide (MoOx), vanadium oxide (VOx), ruthenium oxide (RuOx), or tungstenoxide (WOx) and a benzoxazole derivative, and one or more materials ofan alkali metal, an alkali earth metal, and a transition metal.

It is preferable that a highly electron transporting material is usedfor the second layer 605 formed on the first layer 604. Specifically, ametal complex that has a quinoline skeleton or a benzoquinolineskeleton, as typified by Alq₃, and a mixed ligand complex can be used.More specifically, the highly electron transporting material includesmetal complexes such as Alq₃, Almq₃, BeBq₂, BAlq, Zn(BOX)₂, andZn(BTZ)₂. Further, in addition to the metal complexes, oxadiazolederivatives such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) and1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (OXD-7),triazole derivatives such as3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole (TAZ)and3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(p-EtTAZ), imidazole derivatives such as TPBI, and phenanthrolinederivatives such as bathophenanthroline (BPhen) and bathocuproin (BCP)can be used.

It is preferable that a material that has a large ionization potentialand a large band gap is used for the third layer 606 formed on thesecond layer 605. Specifically, condensed aromatic rings such asperylene derivatives (for example, perylene, alkyl perylene, and arylperylene), anthracene derivatives (for example, alkyl anthracene anddiaryl anthracene), and pyrene derivatives (for example, alkyl pyreneand aryl pyrene) can be used. In addition, metal complexes such asdistyrylarylene, silole derivatives, coumarin derivatives, andbis(2-methyl-8-quinolinolato)-(4-hydroxy-biphenylyl)-aluminum (BAlq) canalso be used. The materials mentioned above can be used as any of adopant and a single layer film.

It is preferable that a known highly hole transporting material that islow in crystallity is used for the fourth layer 607 formed on the thirdlayer 606. Specifically, aromatic amine compounds (that is, a compoundthat has a benzene ring-nitrogen bond) are appropriate, which include4,4′-bis[N-(3-methylphenyl)-N-phenylamino]-biphenyl (TPD) and aderivative thereof such as4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (α-NPD), for example.In addition, starburst aromatic amine compounds such as 4,4′,4″-tris(N,N-diphenylamino)-triphenylamine (TDATA) and MTDATA can also be used.Further, 4,4′,4″-tris (N-carbazolyl)-triphenylamine (abbreviation: TCTA)may be used. Among polymeric materials, a material such as poly(vinylcarbazole) that shows a favorable hole transporting property canbe used.

Further, in the present invention, a highly hole injecting benzoxazolederivative or metal oxide that is resistant to etching is used for thefifth layer 608 formed on the fourth layer 607. Both the metal oxide andthe benzoxazole derivative may be used. By using the material mentionedabove, organic materials included in the first to fourth layers can beprevented from sputter damage when sputtering is later used to form thesecond electrode 603 on the fifth layer 608. The fifth layer 608 can beformed by evaporation. Further, it is preferable that the fifth layer608 has a film thickness of 10 nm or more. In order to suppress damagedue to sputtering, forming to have this film thickness is effective.

For the fifth layer 608, the metal oxide may be used in combination witha highly hole transporting organic material. The highly holetransporting material includes, for example, an aromatic amine compound(that is, a compound that has a benzene ring-nitrogen bond) such as4,4′-bis[N -(1-naphthyl)-N-phenyl-amino]-biphenyl (abbreviation: α-NPD),4,4′-bis[N -(3-methylphenyl)-N-phenyl-amino]-biphenyl (abbreviation:TPD), 4,4′,4″-tris(N,N-diphenyl-amino)-triphenylamine (abbreviation:TDATA), and4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine(abbreviation: MTDATA), without limitation to the materials mentionedhere. Another material may be used. With the above-mentioned structure,crystallization of the fifth layer 608 can be suppressed, and then,reliability of the light-emitting element can be enhanced.

Further, in the case of forming the fifth layer 608 to have a filmthickness of 100 nm or more, short between the first electrode 601 andthe second electrode 603, which is caused due to a factor such as aprojection formed at a film surface of the first electrode 601 or thesecond electrode 603 or a foreign material mixed in between theseelectrodes, can be suppressed.

As the metal oxide, molybdenum oxide (MoOx), vanadium oxide (VOx),ruthenium oxide (RuOx), and tungsten oxide (WOx), for example, can beused specifically.

In the case of using the benzoxazole derivative for the fifth later 608,it is preferable to use one or more materials of TCNQ, FeCl₃, C₆₀, andF₄-TCNQ in combination with the benzoxazole derivative to enhance thehole injecting property.

In the light-emitting element that has the structure described above,blue or light blue luminescence can be obtained from the third layer 606when a voltage is applied between the first electrode 601 and the secondelectrode 603 to supply a current in forward bias to theelectroluminescent layer 602. The light from the third layer 606 seemsto be light blue since blue light is mixed with green light. To give aspecific example, although light obtained from a perylene derivativethat is used for the third layer 606 is basically blue, green light ismixed to get closer to a light blue since excimer luminescence isobserved with increasing a doping concentration. In the presentinvention, by transmitting light obtained from the light-emittingelement through a coloring layer of a color filter, light in thewavelength range corresponding to a green can be shielded to obtainlight that is high in purity of a blue.

Next, another specific example of a light-emitting element of alight-emitting device according to the present invention will bedescribed.

With reference to FIG. 6B, a structure of a light-emitting element fromwhich light in the wavelength range corresponding to a blue can beobtained will be described. The light-emitting element shown in FIG. 6Bhas, over a substrate 610, a first electrode 611, an electroluminescentlayer 612 formed on the first electrode 611, and a second electrode 613formed on the electroluminescent layer 612. In FIG. 6B, the firstelectrode 611 serves as a cathode and the second electrode 613 serves asan anode. The electroluminescent layer 612 has first to fourth layers614 to 617.

It is preferable that a metal, an alloy, an electrically conductivecompound, or a mixture of these, which has a small work function and isgenerally used for a cathode of a light-emitting element is used to formthe first electrode 611, like the first electrode 601 in FIG. 6A. Inaddition, it is preferable that a conductive material that has a largework function is used to form the second electrode 613, like the secondelectrode 603 in FIG. 6A.

It is preferable that a highly electron injecting material is used forthe first layer 614 formed to come in contact with the first electrode611 that serves as a cathode, like the first layer 604 in FIG. 6A. It ispreferable that a highly electron transporting material is used for thesecond layer 615 formed on the first layer 614, like the second layer605 in FIG. 6A. It is preferable that a known highly hole transportingmaterial that is low in crystallity is used for the third layer 616formed on the second layer 615, like the fourth layer 607 in FIG. 6A. Inaddition, a highly hole injecting benzoxazole derivative or metal oxidethat is resistant to etching is used for the fourth layer 617 formed onthe third layer 616, like the fifth layer 608 in FIG. 6A.

Depending on the kind of a dopant added to the second layer 615 or thethird layer 616, green luminescence is obtained or red luminescence isobtained. In order to obtain green luminescence, a material such as acoumarin derivative, a quinacridone derivative, Alq₃, ortris(4-methyl-8-quinolinolato)aluminum (Almq₃) may be added to thesecond layer 615 as a dopant. Other than the materials described above,also in the case of using a triplet material such as a tris(phenylpyridine) iridium complex, green luminescence is obtained. In thecase of using the tris (phenylpyridine) iridium complex as a dopant, itis preferable to used a bipolar material as a host, and further, in thiscase, it is preferable to form a highly hole blocking layer that has asmall ionization potential and a large band gap between the first layer614 and the second layer 615. For forming the highly hole blockinglayer, a phenanthroline derivative such as BCP or oligopyridine, forexample, can be used specifically.

By applying a current in forward bias to the light-emitting element thathas the structure mentioned above, green luminescence is obtained fromthe second layer 615.

In the light-emitting element that has the structure shown in FIG. 6B, acondensed aromatic compound such as rubrene, a perylene diimidederivative, oligothiophene, a DCM derivative typified by4,4-dicyanomethylene-2-methyl-6-(4-diarylamino)styryl-2,5-pyran, a2,5-dicyano-1,4-bis(4-diarylaminostyryl)benzene derivative, abenzocoumarin derivative, a porphyrin-based material such as a platinumoctaethylporphyrin complex, or a rare earth metal complex such as a tris(1-benzoylacetonato) (1,10-phenanthroline) europium complex, forexample, may be added as a dopant to one of the second layer 615 and thethird layer 616 in order to obtain red luminescence.

By applying a current in forward bias to the light-emitting element thathas the structure mentioned above, red luminescence is obtained from thesecond layer 615 or the third layer 616 to which the dopant is added.

Alternatively, a layer including a material that has a large ionizationpotential and a large band gap, to which the dopant mentioned above, maybe provided between the second layer 615 and the third layer 616 toobtain luminescence from the added layer. In this case, it is preferablethat a material such as Alq₃ or a2,5-dicyano-1,4-bis(4-diarylaminostyryl)benzene derivative is used as ahost for the added layer.

The above-mentioned red luminescence, in fact, mixed with green lightmay seem to be orange or yellow. In the present invention, bytransmitting light obtained from the light-emitting element through acoloring layer of a color filter, light in the wavelength rangecorresponding to a green can be shielded to obtain light that is high inpurity of a red.

Further, in the present invention, by using a color filter, two colorsthat have different spectra from each other can also be obtained fromlight of a spectrum. For example, blue light and green light can beextracted selectively from light of a mixture of a blue color and agreen color.

In the case of the light-emitting element that has the structure shownin FIG. 6A, a dopant from which green light can be obtained and a dopantfrom which blue light can be obtained are added to the third layer 606in order to obtain light of a mixture of a blue color and a green color.In the case of the light-emitting element that has the structure shownin FIG. 6B, both a dopant from which green light can be obtained and adopant from which blue light can be obtained are added to the secondlayer 615 in order to obtain light of a mixture of a blue color and agreen color. Alternatively, in the case of the light-emitting elementthat has the structure shown in FIG. 6A, a dopant from which green lightcan be obtained may be added to the second layer 605. In addition, inthe case of the light-emitting element that has the structure shown inFIG. 6A, light of a mixture of a blue color and a green color due toexcimer luminescence can be obtained by using a high concentration ofcondensed aromatic ring that has small steric hindrance (for example,perylene, perylene derivatives, pyrene derivatives, and anthracenederivatives) as a dopant for the third layer 606.

In the case of the light-emitting element that has the structure shownin FIG. 6B, in order to obtain light of a mixture of a red color and agreen color, an electron transporting host such as a metal quinolinolecomplex typified by Alq₃ may be used for the second layer 615, and adopant from which red light can be obtained may further be added to thesecond layer 615. In the case of the light-emitting element that has thestructure shown in FIG. 6A, a bipolar host may be used for the thirdlayer 606, and a dopant from which green light can be obtained mayfurther be added to the third layer 606. Further, an electrontransporting host may be used for the second layer 605, and a dopantfrom which red light can be obtained may further be added to the secondlayer 605.

In each case of FIGS. 6A and 6B, the first electrode serves as a cathodeand the second electrode serves as an anode. However, the firstelectrode and the second electrode may serve as an anode and a cathode,respectively.

FIG. 6C shows a structure of a light-emitting element as an example,where a first electrode serves as an anode and a second electrode servesas a cathode. The light-emitting element shown in FIG. 6C has, over asubstrate 620, a first electrode 621, an electroluminescent layer 622formed on the first electrode 621, and a second electrode 623 formed onthe electroluminescent layer 622. In FIG. 6C, the first electrode 621serves as an anode and the second electrode 623 serves as a cathode.

In the case of FIG. 6C, in addition to a single layer film including oneor more of materials such as TiN, ZrN, Ti, W, Ni, Pt, Cr, and Ag, alamination layer including a titanium nitride film and a film containingaluminum as its main component, and a three-layer structure including atitanium nitride film, a film containing aluminum as its main component,and a titanium nitride film can be used as the first electrode 621.Further, a transparent conductive film such as ITO, ITSO, or IZO may belaminated on the above-mentioned material that can reflect light for useas the first electrode 621. In FIG. 6C, an Al—Si film 630, a Ti film631, and an ITO film 632 are laminated in this order over the glasssubstrate 620 to form the first electrode 621.

Further, as the second electrode 623, a transparent conductive film suchas ITO, IZO, ITSO is used.

The electroluminescent layer 622 has a plurality of layers like FIG. 6Aor 6B. However, the order of laminating the respective layers is reversein FIG. 6C. FIG. 6C shows a case where the electroluminescent layer 622has first to fifth layers 624 to 628.

It is preferable that a material that has a relatively small ionizationpotential is used for the first layer 624 formed to come in contact withthe first electrode 621 that serves as an anode. The material is roughlyclassified into metal oxides, a low molecular weight organic compound,or a high molecular weight organic compound. In the case of the metaloxide, vanadium oxide, molybdenum oxide, ruthenium oxide, and aluminumoxide, for example, can be used. In the case of the low molecular weightorganic compound, starburst amines typified by m-MTDATA, metalphthalocyanines typified by copper phthalocyanine (abbreviation: CuPc),phthalocyanine (abbreviation: H₂Pc), and 2,3-dioxyethylenethiophenederivatives for example, can be used. The low molecular weight organiccompound and the metal oxide described above may be co-evaporated toform the first layer 624. In the case of the high molecular weightorganic compound, polymers such as polyanilines (abbreviation: PAni),polyvinyl carbazoles (abbreviation: PVA), and polythiophene derivativescan be used. Polyethylene dioxythiophene (abbreviation: PEDOT) that isone of the polythiophene derivatives, which is doped with polystyrenesulfonate (abbreviation: PSS) may be used. A benzoxazole derivative andone or more materials of TCNQ, FeCl₃, C₆₀, and F₄-TCNQ may be used incombination.

It is preferable that a known highly hole transporting material that islow in crystallity is used for the second layer 625 formed on the firstlayer 624. Specifically, the materials that can be used for the fourthlayer 607 in FIG. 6A can be used in the same way.

It is preferable that a material that has a large ionization potentialand a large band gap is used for the third layer 626 formed on thesecond layer 625. Specifically, the materials that can be used for thethird layer 606 in FIG. 6A can be used in the same way.

It is preferable that a highly electron transporting material is usedfor the fourth layer 627 formed on the third layer 626. Specifically,the materials that can be used for the second layer 605 in FIG. 6A canbe used in the same way.

In addition, in the present invention, a benzoxazole derivative or ametal oxide that is resistant to etching is used for the fifth layer 628formed on the fourth layer 627. In addition, in order to enhance anelectron injecting property, one or more materials of an alkali metal,an alkali earth metal, and a transition metal is used in combinationwith the material mentioned above. Both the metal oxide and thebenzoxazole derivative may be used. By using the material mentionedabove, organic materials included in the first to fourth layers can beprevented from sputter damage when sputtering is later used to form thesecond electrode 623 on the fifth layer 628. The fifth layer 628 can beformed by evaporation. Further, it is preferable that the fifth layer628 has a film thickness of 10 nm or more. In order to suppress damagedue to sputtering, forming to have this film thickness is effective.

Further, in the case of forming the fifth layer 628 to have a filmthickness of 100 nm or more, short between the first electrode 621 andthe second electrode 623, which is caused due to a factor such as aprojection formed at a film surface of the first electrode 621 or thesecond electrode 623 or a foreign material mixed in between theseelectrodes, can be suppressed.

As the metal oxide, molybdenum oxide (MoOx), vanadium oxide (VOx),ruthenium oxide (RuOx), and tungsten oxide (WOx), for example, can beused specifically.

In the light-emitting element shown in FIG. 6C, as in FIG. 6B,luminescence may be obtained from the second layer 625 or the fourthlayer 627 by adding a dopant without providing the third layer 626.

EMBODIMENT 4

In the present embodiment, a form will be described, which is astructure of a pixel of a light-emitting device according to the presentinvention.

FIG. 7 shows a cross-sectional view of a light-emitting device in thepresent embodiment. In FIG. 7, transistors 7001 to 7003 are formed overa substrate 7000. The transistors 7001 to 7003 are covered with a firstinterlayer insulating film 7004, and wirings 7005 to 7007 are formed onthe first interlayer insulating film 7004, which are electricallyconnected to drains of the transistors 7001 to 7003 through contactholes, respectively.

Further, a second interlayer insulating film 7008 and a third interlayerinsulating film 7009 are laminated on the first interlayer insulatingfilm 7004 to cover the wirings 7005 to 7007. For the first interlayerinsulating film 7004 and the second interlayer insulating film 7008, anorganic resin film, an inorganic insulating film, and an insulating filmincluding a Si—O bond and a Si—CHx bond, which is formed by using amaterial including a siloxane material as a starting material, forexample can be used. In the present embodiment, a non-photoseneitiveacrylic is used. As the third interlayer insulating film 7009, a filmthat hardly allows permeation of a material such as moisture or oxygen,which is a cause to promote deterioration of a light-emitting element,as compared with other insulating films, is used. Typically, it ispreferable to use a DLC film, a carbon nitride film, or a siliconnitride film formed by RF sputtering, for example.

On the third interlayer insulating film 7009, wirings 7010 to 7012 areformed, which are electrically connected to the wirings 7005 to 7007through contact holes respectively. A portion of each of the wirings7010 to 7012 functions as a first electrode of a light-emitting element.In FIG. 7, unlike the pixel shown in FIG. 2, the first electrode and thewiring electrically connected to the TFT are formed in different layers.Therefore, the first electrode can be arranged to have a larger area,hence a light-emitting element is allowed to have a larger region fromwhich light can be obtained.

Further, a film such as an insulating film including a Si—O bond and aSi—CHx bond, which is formed by using a material including a siloxanematerial as a starting material, an organic resin film, or inorganicinsulating film is used to form a partition 7013 on the third interlayerinsulating film 7009. The partition 7013 has openings, and the wirings7010 to 7012 that function as the first electrodes, electroluminescentlayers 7014 to 7016, and a second electrode 7017 are overlapped in theopenings to form light-emitting elements 7018 to 7020, respectively.Each of the electroluminescent layers 7014 to 7016 has a laminatedstructure including a plurality of layers. A protective film may beformed on the partition 7013 and the second electrode 7017. In thiscase, a film that hardly allows permeation of a material such asmoisture or oxygen, which is a cause to promote deterioration of alight-emitting element, as compared with other insulating films, is usedas the protective film. Typically, it is preferable to use a DLC film, acarbon nitride film, or a silicon nitride film formed by RF sputtering,for example. In addition, as the protective film, it is also possible touse a laminate film including the above-mentioned film that hardlyallows permeation of a material such as moisture or oxygen and a filmthat easily allows permeation of a material such as moisture or oxygenas compared with the above-mentioned film.

Before deposition of the electroluminescent layers 7014 to 7016, thepartition 7013 is heated in an atmosphere of a vacuum in order to removeadsorbed moisture or oxygen. Specifically, a heat treatment is performedin an atmosphere of a vacuum at 100° C. to 200° C. for approximately 0.5to 1 hour. Preferably, the vacuum is 3×10⁻⁷ Torr or less, and it is mostpreferable to be preferably 3×10⁻⁸ Torr or less if possible. In the casewhere the electroluminescent layers 7014 to 7016 are deposited afterperforming a heat treatment in an atmosphere of a vacuum to thepartition 7013, reliability can further enhanced by keep the atmosphereof the vacuum until just before the deposition.

It is preferable that an edge of the partition 7013 in the opening isrounded to prevent a hole from being made in the electroluminescentlayers 7014 to 7016 formed on the partition 7013 to partially overlap.Specifically, it is preferable that a curve described by a cross sectionof the partition 7013 in the opening has a curvature radius of 0.2 to 2μm.

With the above-mentioned structure, the electroluminescent layers 7014to 7016 and the second electrode 7017, which are later formed, can havefavorable coverages, and the wirings 7010 to 7012 and the secondelectrode 7017 can be prevented from being shorting out at a hole madein the electroluminescent layers 7014 to 7016. Further, by stressrelaxation for the electroluminescent layers 7014 to 7016, a defect of areduced light-emitting region, which is referred to as shrinking, can bereduced, hence reliability can be enhanced.

FIG. 7 shows an example of using a positive photosensitive acrylic resinas the partition 7013. A photosensitive organic resin is classified intoa positive photosensitive organic resin in which a portion exposed by anenergy line such as light, electrons, or ions is removed or a negativephotosensitive organic resin in which an exposed portion is left. In thepresent invention, a negative organic resin film may be used. Aphotosensitive polyimide may be used to form the partition 7013. In thecase of using a negative acrylic to form the partition 7013, an edge inthe opening has a S-shaped cross section. In this case, it is preferablethat a top portion and a bottom portion in the opening have a curvatureradius of 0.2 to 2 μm.

For the wirings 7010 to 7012, a material that transmits no light isused, and for planarization of surfaces thereof, polishing may beperformed by CMP or cleaning with a polyvinyl-alcohol-based porousmaterial may be performed. After polishing by CMP, the surfaces of thewirings 7010 to 7012 may be subjected to a treatment such as ultravioletirradiation and oxygen plasma treatment.

Further, reference numeral 7021 denotes a covering material for sealingof the light-emitting elements 7018 to 7020, which has alight-transmitting property. Adjacent to the covering material 7021, ashielding film 7022 for shielding visible light and a color filter 7026that has coloring layers 7023 to 7025 corresponding to pixelscorresponding to respective colors are formed. In the case of FIG. 7,light in the wavelength range corresponding to a red, of light emittedfrom the light-emitting element 7018, is selectively transmitted throughthe coloring layer 7023, light in the wavelength range corresponding toa green, of light emitted from the light-emitting element 7019, isselectively transmitted through the coloring layer 7024, and light inthe wavelength range corresponding to a blue, of light emitted from thelight-emitting element 7020, is selectively transmitted through thecoloring layer 7025.

In FIG. 7, a black pigment and a desiccant are dispersed in a resin toform the shielding film 7022. With this structure, deterioration of thelight-emitting elements can be prevented.

The shielding film 7022 is arranged to overlap a portion between thelight-emitting elements, such as a portion between the light-emittingelements 7018 and 7019 and a portion between the light-emitting elements7019 and 7020, and is able to prevent light from the light-emittingelement from being transmitted through the coloring layer correspondingto the adjacent pixel.

In FIG. 7, the electroluminescent layer 7014, 7015, or 7016 that has adifferent electroluminescent material included or a different elementstructure is used depending on the pixel corresponding to each color.However, the present invention is not always limited to this structure.In at least pixels corresponding to two colors respectively,electroluminescent layers that have different electroluminescentmaterials included or different element structures from each other areused respectively.

In the present invention, a transparent conductive film such as ITO,ITSO, or IZO, mentioned above, is used for the second electrode 7017formed on the electroluminescent layers 7014 to 7016, which is formed bysputtering. In each of the electroluminescent layers 7014 to 7016, thetop layer in contact with the second electrode 7017 includes at leastone of a metal oxide and a benzoxazole derivative.

An enclosed space formed by the covering material 7021 and the substrate7000 may be filled with an inert gas or a resin, or a hygroscopicmaterial (barium oxide, for example) may be arranged inside. FIG. 8shows a state of the light-emitting device shown in FIG. 2, where theenclosed space formed by the substrate and the covering material isfilled with a resin 8001 in which a desiccant 8002 is dispersed. Asshown in FIG. 8, reliability of the light-emitting element is improvedby dispersing the desiccant inside.

In each of FIGS. 2 and 8, the color filter is provided adjacent to thecovering material. However, the present invention is not limited to thisstructure. For example, as shown in FIG. 9, coloring layers 904 to 906may be formed by a method such as inkjet to overlap with light-emittingelements 901 to 903. In this case, for sealing of the light-emittingelements 901 to 903, a resin can be used instead of a covering material.Therefore, a light extraction efficiency can be enhanced as comparedwith a case of providing a covering material.

The present invention is not limited to the manufacturing methodmentioned above. A known method can be used to manufacture thelight-emitting device according to the present invention.

EMBODIMENT 5

A transistor that is used for a light-emitting device according to thepresent invention may be a TFT using a polycrystalline semiconductor ora TFT using an amorphous or semi-amorphous semiconductor. In the presentembodiment, a structure of a TFT formed by using an amorphoussemiconductor or a semi-amorphous semiconductor will be described.

FIG. 10A shows a cross-sectional view of a TFT that is used in a drivercircuit and a cross-sectional view of a TFT that is used in a pixelportion. Reference numeral 1001 denotes the cross-sectional view of theTFT that is used in the driver circuit, reference numeral 1002 denotesthe cross-sectional view of the TFT that is used in the pixel portion,and reference numeral 1003 denotes a cross-sectional view of alight-emitting element to which a current is supplied by the TFT 1002.The TFTs 1001 and 1002 are inversely staggered TFTs (bottom-gate TFTs).

The TFT 1001 of the driver circuit has a gate electrode 1010 formed overa substrate 1000, a gate insulating film 1011 covering the gateelectrode 1010, a first semiconductor film 1012 formed to include asemi-amorphous semiconductor or an amorphous semiconductor, which isoverlapped with the gate electrode 1010 while the gate insulating film1011 is interposed in between. Further, the TFT 1001 has a pair ofsecond semiconductor films 1013 that function as a source region and adrain region and a third semiconductor film 1014 provided between thefirst semiconductor film 1012 and each of the second semiconductor films1013.

In FIG. 10A, the gate insulating film 1011 has two layers of insulatingfilms. However, the present invention is not limited to this structure.The gate insulating film 1011 may have a single-layered insulating filmor three or more layers of insulating films.

The second semiconductor films 1013 are formed to include an amorphoussemiconductor or a semi-amorphous semiconductor, and doped with animpurity that imparts one conductivity type. The pair of secondsemiconductor films 1013 is faced with each other while a channelforming region of the first semiconductor film 1012 is interposed inbetween.

The third semiconductor film 1014 is formed to include an amorphoussemiconductor or a semi-amorphous semiconductor, has the sameconductivity type as that of the second semiconductor films 1013, andhas a property of having a lower conductivity than the secondsemiconductor film 1013. Since the third semiconductor film 1014functions as an LDD region, an electric field concentrated at an edge ofthe second semiconductor film 1013 that functions as a drain region isreduced to enable preventing hot carrier effect. It is not alwaysnecessary to provide the third semiconductor film 1014. However, byproviding the third semiconductor film 1014, it is possible to enhancewithstand voltage of the TFT and improve reliability. In the case wherethe TFT 1001 is an n-type TFT, n-type conductivity can be obtainedwithout particular doping with an impurity that imparts n-typeconductivity in forming the third semiconductor film 1014. Therefore, inthe case where the TFT 1001 is an n-type TFT, it is not always necessaryto dope the third semiconductor film 1014 with an n-type impurity.However, in this case, the first semiconductor film 1012 where a channelis formed is doped with an impurity that imparts p-type conductivity tocontrol the conductivity type so as to be closer to an i-typesemiconductor as much as possible.

Further, two wirings 1015 are formed to come in contact with the pair ofsecond semiconductor films 1013. One of the wirings 1015 is connected toan IC chip 1051 through an anisotropic conductive resin 1050. In orderto form the IC chip 1051, a single-crystal semiconductor may be used ora poly crystalline semiconductor formed over a glass substrate may beused. By arranging the IC chip 1051 to be overlapped with a sealingmaterial 1052 that is used for sealing of a light-emitting element, aregion at the periphery of the pixel portion can be reduced in size.

The TFF 1002 of the pixel portion has a gate electrode 1020 formed overa substrate 1000, the gate insulating film 1011 covering the gateelectrode 1020, a first semiconductor film 1022 formed to include asemi-amorphous semiconductor or an amorphous semiconductor, which isoverlapped with the gate electrode 1020 while the gate insulating film1011 is interposed in between. Further, the TFT 1002 has a pair ofsecond semiconductor films 1023 that function as a source region and adrain region and a third semiconductor film 1024 provided between thefirst semiconductor film 1022 and each of the second semiconductor films1023.

The second semiconductor films 1023 are formed to include an amorphoussemiconductor or a semi-amorphous semiconductor, and doped with animpurity that imparts one conductivity type. The pair of secondsemiconductor films 1023 is faced with each other while a channelforming region of the first semiconductor film 1022 is interposed inbetween.

The third semiconductor film 1024 is formed to include an amorphoussemiconductor or a semi-amorphous semiconductor, has the sameconductivity type as that of the second semiconductor films 1023, andhas a property of having a lower conductivity than the secondsemiconductor film 1023. Since the third semiconductor film 1024functions as an LDD region, an electric field concentrated at an edge ofthe second semiconductor film 1023 that functions as a drain region isreduced to enable preventing hot carrier effect. It is not alwaysnecessary to provide the third semiconductor film 1024. However, byproviding the third semiconductor film 1024, it is possible to enhancewithstand voltage of the TFT and improve reliability. In the case wherethe TFT 1002 is an n-type TFT, n-type conductivity can be obtainedwithout particular doping with an impurity that imparts n-typeconductivity in forming the third semiconductor film 1024. Therefore, inthe case where the TFT 1002 is an n-type TFT, it is not always necessaryto dope the third semiconductor film 1024 with an n-type impurity.However, in this case, the first semiconductor film 1022 where a channelis formed is doped with an impurity that imparts p-type conductivity tocontrol the conductivity type so as to be closer to an i-typesemiconductor as much as possible.

Further, wirings 1025 are formed to come in contact with the pair ofsecond semiconductor films 1023.

In addition, a first passivation film 1040 and a second passivation film1041 that are insulating films are formed to cover the TFTs 1001 and1002 and the wirings 1015 and 1025. Other than the two layers, thepassivation film covering the TFTs 1001 and 1002 may be a single layeror may have three layers or more. For example, the first passivationfilm 1040 can be formed to include silicon nitride, and the secondpassivation film 1041 can be formed to include silicon oxide. By formingthe passivation film to include silicon nitride or silicon oxynitride,the TFTs 1001 and 1002 can be prevented from being degraded due tomoisture or oxygen.

One of the wirings 1025 is connected to a first electrode 1030 of thelight-emitting element 1003. Further, an electroluminescent layer 1031is formed to come in contact with the first electrode 1030, and a secondelectrode 1032 is formed to come in contact with the electroluminescentlayer 1032.

Next, a structure of a TFT of a light-emitting device according to thepresent invention, which is different from FIG. 10A, will be described.FIG. 10B shows a cross-sectional view of a TFT that is used in a drivercircuit and a cross-sectional view of a TFT that is used in a pixelportion. Reference numeral 1101 denotes the cross-sectional view of theTFT that is used in the driver circuit, reference numeral 1102 denotesthe cross-sectional view of the TFT that is used in the pixel portion,and reference numeral 1103 denotes a cross-sectional view of alight-emitting element to which a current is supplied by the TFT 1102.

The TFT 1101 of the driver circuit and the TFT 1102 of the pixel portionrespectively have gate electrodes 1110 and 1120, a gate insulating film1111 covering the gate electrodes 1110 and 1120, and first semiconductorfilms 1112 and 1122 formed to include a semi-amorphous semiconductor oran amorphous semiconductor, which are respectively overlapped with thegate electrodes 1110 and 1120 while the gate insulating film 1111 isinterposed in between. In addition, channel protective films 1160 and1161 that are insulating films are formed to cover channel formingregions of the first semiconductor films 1112 and 1122, respectively.The channel protective films 1160 and 1161 are provided for preventingthe channel forming regions of the first semiconductor films 1112 and1122 from being etched in manufacturing processes of the TFTs 1101 and1102, respectively. Further, the TFT 1101 has a pair of secondsemiconductor films 1113 that function as a source region and a drainregion and a third semiconductor film 1114 provided between the firstsemiconductor film 1112 and each of the second semiconductor films 1113,and the TFF 1102 has a pair of second semiconductor films 1123 thatfunction as a source region and a drain region and a third semiconductorfilm 1124 provided between the first semiconductor film 1122 and each ofthe second semiconductor films 1123.

In FIG. 10B, the gate insulating film 1111 has two layers of insulatingfilms. However, the present invention is not limited to this structure.The gate insulating film 1111 may have a single-layered insulating filmor three or more layers of insulating films.

The second semiconductor films 1113 and 1123 are formed to include anamorphous semiconductor or a semi-amorphous semiconductor, and dopedwith an impurity that imparts one conductivity type. The pair of secondsemiconductor films 1113 is faced with each other while the channelforming region of the first semiconductor film 1112 is interposed inbetween, and the pair of second semiconductor films 1123 is faced witheach other while the channel forming region of the first semiconductorfilm 1122 is interposed in between.

The third semiconductor films 1114 and 1124 are formed to include anamorphous semiconductor or a semi-amorphous semiconductor, have the sameconductivity type as those of the second semiconductor films 1113 and1123, and have a property of having a lower conductivity than the secondsemiconductor films 1113 and 1123, respectively. Since the thirdsemiconductor films 1114 and 1124 respectively function as LDD regions,electric fields respectively concentrated at edges of the secondsemiconductor films 1113 and 1123 that respectively function drainregions are reduced to enable preventing hot carrier effect. It is notalways necessary to provide the third semiconductor films 1114 and 1124.However, by providing the third semiconductor films 1114 and 1124, it ispossible to enhance withstand voltage of the TFTs and improvereliability. In the case where the TFTs 1101 and 1102 are n-type TFTs,n-type conductivity can be obtained without particular doping with animpurity that imparts n-type conductivity in forming the thirdsemiconductor films 1114 and 1124. Therefore, in the case where the TFTs1101 and 1102 are n-type TFTs, it is not always necessary to dope thethird semiconductor films 1114 and 1124 with an n-type impurity.However, in this case, the first semiconductor films 1112 and 1122 wherea channel is formed are doped with an impurity that imparts p-typeconductivity to control the conductivity type so as to be closer to ani-type semiconductor as much as possible.

Further, two wirings 1115 and two wirings 1125 are formed to come incontact with the pair of the second semiconductor films 1113 and thepair of the second semiconductor films 1123, respectively. One of thewirings 1115 is connected to an IC chip 1151 through an anisotropicconductive resin 1150. In order to form the IC chip 1151, asingle-crystal semiconductor may be used or a poly crystallinesemiconductor formed over a glass substrate may be used. By arrangingthe IC chip 1151 to be overlapped with a sealing material 1152 that isused for sealing of a light-emitting element, a region at the peripheryof the pixel portion can be reduced in size.

In addition, a first passivation film 1140 and a second passivation film1141 that are insulating films are formed to cover the TFTs 1101 and1102 and the wirings 1115 and 1125. Other than the two layers, thepassivation film covering the TFTs 1101 and 1102 may be a single layeror may have three layers or more. For example, the first passivationfilm 1140 can be formed to include silicon nitride, and the secondpassivation film 1141 can be formed to include silicon oxide. By formingthe passivation film to include silicon nitride or silicon oxynitride,the TFTs 1101 and 1102 can be prevented from being degraded due tomoisture or oxygen.

One of the wirings 1125 is connected to a first electrode 1130 of thelight-emitting element 1103. Further, an electroluminescent layer 1131is formed to come in contact with the first electrode 1130, and a secondelectrode 1132 is formed to come in contact with the electroluminescentlayer 1131.

The present embodiment describes an example where a driver circuit and apixel portion of a light-emitting device are formed over one substratewith the use of a TFT using a semi-amorphous semiconductor or anamorphous semiconductor. However, the present invention is not limitedto this structure. When a pixel portion is formed with the use of a TFTusing a semi-amorphous semiconductor or an amorphous semiconductor, aseparately formed driver circuit may be attached to the substrate overwhich a pixel portion is formed.

Besides, a component such as a gate electrode or a wiring may be formedby inkjet. FIG. 11A shows a cross-sectional of a pixel formed by usinginkjet as an example. In FIG. 11A, reference numeral 1201 denotes abottom-gate TFT, which is electrically connected to a light-emittingelement 1202. The TFT 1201 has a gate electrode 1203, a gate insulatingfilm 1204 formed on the gate electrode 1203, a first semiconductor film1205 formed on the gate insulating film 1204, and a second semiconductorfilm 1206 formed on the first semiconductor film 1205. The firstsemiconductor film 1205 functions as a channel forming region. Thesecond semiconductor film 1206 is doped with an impurity that impartsone conductivity type to function as a source or a drain.

In addition, a wiring 1208 is formed to come in contact with the secondsemiconductor film 1206, and the wiring 1208 is connected to a firstelectrode 1209 of the light-emitting element 1202. The light-emittingelement 1202 has the first electrode 1209, an electroluminescent layer1210 formed on the first electrode 1209, and a second electrode 1211formed on the electroluminescent layer 1210.

In the case of a light-emitting device shown in FIG. 11A, componentssuch as the gate electrode 1203, the wiring 1208, the first electrode1209, the electroluminescent layer 1210, a mask that is used for patternformation can be formed by inkjet.

FIG. 11B also shows a cross-sectional of a pixel formed by using inkjetas an example. In FIG. 11B, an insulating film (an etching stopper) 1224that is able to prevent a first semiconductor film 1221 from beingetched in patterning of a second semiconductor film 1222 and a wiring1223 is formed on a first semiconductor film 1221 of a bottom-gate TFT1220.

EMBODIMENT 6

In a light-emitting device according to the present invention, atransparent conductive film is used as a second electrode that is formedon an electroluminescent layer. In general, a transparent conductivefilm typified by ITO, ITSO, and IZO tends to have a lower conductivityas compared to a metal such as Al. When the second electrode has ahigher sheet resistance, a luminance is decreased due to a voltage drop,which is unfavorable. Consequently, in the present invention, in orderto suppress the voltage drop, a material that has a higher conductivitythan the second electrode may be used to form an auxiliary electrode onthe second electrode.

FIG. 12 shows a cross-sectional view of a light-emitting deviceaccording to the present invention, where an auxiliary electrode isformed. In FIG. 12, reference numeral 1301 denotes a light-emittingelement, and reference numeral 1302 denotes a transistor for supplying acurrent to the light-emitting element 1301. In addition, referencenumerals 1303, 1304, and 1305 denote a first electrode, anelectroluminescent layer, and a second electrode, respectively. In anopening of a partition 1306, a portion where the first electrode 1303,the electroluminescent layer 1304, and the second electrode 1305 areoverlapped with each other corresponds to the light-emitting element1301.

The second electrode 1305 is formed to include a transparent conductivefilm typified by ITO, ITSO, and IZO, and has a light-transmittingproperty. On the second electrode 1305, an auxiliary electrode 1307 isfurther formed. Specifically, the auxiliary electrode 1307 is formed ina region overlapped with the partition 1306.

The combined resistance of the second electrode 1305 and the auxiliaryelectrode 1307 is lower than the resistance of only the second electrode1305. Accordingly, a luminance can be prevented from being decreased dueto a voltage drop by forming the auxiliary electrode 1307.

EMBODIMENT 7

In the present embodiment, an appearance of a panel corresponding to aform of a light-emitting device according to the present invention willbe described with reference to FIGS. 13A and 13B. FIG. 13A is a top viewof a panel in which a transistor and a light-emitting element that areformed over a substrate are encapsulated between a covering material andthe substrate with a sealing material, and FIG. 13B corresponds to across-sectional view taken along line A-A′ in FIG. 14A.

A sealing material 4005 is provided to surround a pixel portion 4002, asignal line driver circuit 4003, and a scan line driver circuit 4004that are provided over a substrate 4001. Further, a cover material 4006is provided over the pixel portion 4002, the signal line driver circuit4003, and the scan line driver circuit 4004. Accordingly, the pixelportion 4002, the signal line driver circuit 4003, and the scan linedriver circuit 4004 are encapsulated together with a filling material4007 by the substrate 4001, the sealing material 4005, and the coveringmaterial 4006.

The pixel portion 4002, the signal line driver circuit 4003, and thescan line driver circuit 4004 that are provided over the substrate 4001have a plurality of transistors. In FIG. 13B, transistors 4008 and 4009included in the signal line driver circuit 4003 and a transistor 4010included in the pixel portion 4002 are shown.

In addition, reference numeral 4011 denotes a light-emitting element,which is electrically connected to a transistor 4010.

A leading wiring 4014 corresponds to a wiring for supplying a signal ora power supply voltage to the pixel portion 4002, the signal line drivercircuit 4003, and the scan line driver circuit 4004. The leading wiring4014 is connected to a connecting terminal 4016 through a leading wiring4015. The connecting terminal 4016 is electrically connected to aterminal of an FPC 4018 through an anisotropic conductive film 4019.

As the substrate 4001, in addition to glass, metal (typically,stainless), and ceramics, a flexible as typified by a plastic can beused. As the plastic, an FRP (Fiberglass-Reinforced Plastics) board, aPVF (polyvinylfluoride) film, a Mylar film, a polyester film, or anacrylic resin film can be used. A sheet that has a structure of aluminumfoil sandwiched between PVF films or Mylar films can also be used. Asthe covering material 4006, a light-transmitting material such as aglass plate, a plastic plate, a polyester film, or acrylic film is used.

Adjacent to the covering material 4006, a color filter 4017 that has acoloring layer 4012 and a shielding film 4013 is formed. Of lightemitted from the light-emitting element 4011, light in a specificwavelength range is selectively extracted through the coloring layer4012.

As the filling material 4007, in addition to an inert gas such asnitrogen or argon, ultraviolet curable resin or a thermosetting resinsuch as PVC (polyvinyl chloride), acrylic, polyimide, epoxy resin,silicone resin, PVB (polyvinyl butyral), or EVA (ethylene vinyl acetate)can be used. In the present embodiment, nitrogen is used as the fillingmaterial.

Further, in order to expose the filling material 4007 to a hygroscopicmaterial (preferably, barium oxide) or a material that can absorboxygen, a side of the covering material 4006, facing the substrate 4001,may have a concavo portion 4007 provided to arrange a hygroscopicmaterial or a material that can absorb oxygen.

EMBODIMENT 8

A light-emitting device according to the present invention is high incolor purity and is high in light extraction efficiency for the powerconsumption, and the contrast of an image can be enhanced. Therefore,clear images can be displayed while suppressing power consumption evenwhen the light-emitting device is irradiated with outside light such assunlight, which has the big advantage that the light-emitting device canbe used relatively without selecting a place for the use of thelight-emitting device. Accordingly, the light-emitting device isappropriate for devices such as portable electronic devices, in additionto a television.

Specifically, electronic devices using a light-emitting device accordingto the present invention include a video camera, a digital camera, agoggle-type display (head mount display), a navigation system, a soundreproduction device (such as an in-car audio system or an audio set), alaptop personal computer, a game machine, a personal digital assistant(such as a mobile computer, a cellular phone, a portable game machine,or an electronic book), an image reproduction device equipped with arecording medium (specifically, a device equipped with a display devicethat is able to reproduce a recording medium such as a digital versatiledisc (DVD) and display the image) can be given. FIGS. 14A to 14C showspecific examples of these electronic devices.

FIG. 14A is a display device, which includes a frame body 2001, adisplay portion 2003, a speaker portion 2004, and a video input terminal2005. The display device according to the present invention is completedby using a light-emitting device according to the present invention forthe display portion 2003. The light-emitting device needs no backlightso that the display portion can be made thinner than a liquid crystaldisplay. The display device includes all devices for displayinginformation such as for a personal computer, for receiving TV broadcasting, and for displaying an advertisement.

FIG. 14B is a laptop personal computer, which includes a main body 2201,a frame body 2202, a display portion 2203, a keyboard 2204, an externalconnection port 2205, and a pointing mouse 2206. The image reproductiondevice according to the present invention is completed by using alight-emitting device according to the present invention for the displayportion 2203.

FIG. 14C is a portable image reproduction device equipped with arecording medium (specifically, a DVD reproduction device), whichincludes a main body 2401, a frame body 2402, a display portion A 2403,a display portion B 2404, a recording medium (such as DVD) readingportion 2405, an operation key 2406, and a speaker portion 2407. Thedisplay portion A 2403 is used mainly for displaying image informationwhile the display portion B 2404 is used mainly for displaying characterinformation. The image reproduction device equipped with the recordingmedium also includes a home game machine. The laptop personal computeraccording to the present invention is completed by using alight-emitting device according to the present invention for the displayportion A 2403 and the display portion B 2404.

As described above, the present invention is quite widely applied, andcan be used for electric devices in all fields. In addition, theelectronic devices in the present invention may use a light-emittingdevice that has any of the structures described in Embodiments 1 to 7.

This application is based on Japanese Patent Application serial no.2003-346053 filed in Japan Patent Office on 3 Oct. 2003, the contents ofwhich are hereby incorporated by reference.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless such changes andmodifications depart from the scope of the present invention hereinafterdefined, they should be constructed as being included therein.

1. A light-emitting device comprising: a first light-emitting elementthat emits red light; a second light-emitting element that emits greenlight; a third light-emitting element that emits blue light; a colorfilter, wherein the color filter comprises a first coloring layer thatselectively transmits red light, a second coloring layer thatselectively transmits green light, a third coloring layer thatselectively transmits blue light, and a shielding film, wherein thefirst to third light-emitting elements respectively correspond to thefirst to third coloring layers, wherein the first to thirdlight-emitting elements are separated by a partition, wherein theshielding film is overlapped with the partition, wherein each of thefirst to third light-emitting elements has a first electrode, anelectroluminescent layer formed on the first electrode, and a secondelectrode formed on the electroluminescent layer, and wherein theelectroluminescent layer includes a layer in contact with the secondelectrode, and a metal oxide and a benzoxazole derivative is included inthe layer in contact with the second electrode.
 2. The light-emittingdevice according to claim 1, wherein the first electrode serves as acathode and the second electrode serves as an anode, and a transparentconductive film is used as the second electrode.
 3. The light-emittingdevice according to claim 2, wherein the transparent conductive filmcomprises one of indium tin oxide, indium tin oxide containing silicon,and indium zinc oxide.
 4. The light-emitting device according to claim1, wherein the layer in contact with the second electrode furthercomprises one or more of tetracyanoquinodimethane, FeCl₃, C₆₀, and2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane in addition to themetal oxide and the benzoxazole derivative.
 5. The light-emitting deviceaccording to claim 1, wherein the first electrode serves as an anode andthe second electrode serves as a cathode, and a transparent conductivefilm is used as the second electrode.
 6. The light-emitting deviceaccording to claim 5, wherein the transparent conductive film comprisesone of indium tin oxide, indium tin oxide containing silicon, and indiumzinc oxide.
 7. The light-emitting device according to claim 1, whereinthe layer in contact with the second electrode further comprises one ormore of an alkali metal, an alkali earth metal, and a transition metalin addition to the metal oxide and the benzoxazole derivative.